A polyarylene sulfide (hereinafter may be abbreviated as PAS) is a resin having favorable characteristics as engineering plastic, such as excellent heat resistance, barrier property, chemical resistance, moist heat resistance and flame retardancy. Especially a polyphenylene sulfide (hereinafter may be abbreviated as PPS) is moldable to various molded parts, films, sheets, fibers and the like by injection molding or extrusion molding and are widely used in fields requiring heat resistance and chemical resistance, such as various electric and electronic parts, mechanical parts and automobile parts.
The PPS resin, however, has poorer impact resistance, toughness and molding processability than engineering plastics such as nylon, polycarbonate and polybutylene terephthalate. In order to solve these properties, compounding with different polymers has been tried conventionally. Typical compounding techniques include a method of blending PAS with another different polymer to produce a polymer alloy and a method of producing a block copolymer by chemical bonding of PAS with a different polymer. Among them, block copolymerization allows for formation of the more homogeneous and finer phase separated structure than the other compounding techniques and has thus been extensively studied as the PPS modifying technique. For example, Patent Document 1 discloses a PPS copolymer including a polysulfone component block. This copolymer has the better bending strength and impact resistance, compared with a simple blended mixture. This copolymer is produced by a technique of first synthesizing a polysulfone having chloro groups at both terminals and subsequently performing polycondensation of PPS in the presence of the polysulfone having chloro terminal groups. This technique, however, has a problem that generation and contamination of a homopolymer and non-conformity of block composition distribution are inevitable in principle. There is accordingly still a problem to obtain a homogeneous copolymer.
Other disclosed copolymerization components with PPS include, for example, polyphenylene sulfide ketone (Patent Documents 2 and 3), polyether sulfone (see, for example, Patent Document 4 and Non-Patent Document 1), polysulfide sulfone (see, for example, Patent Document 5), poly(phenylene ether ether ketone) (see, for example, Patent Documents 6 and 7), polyether imide (see, for example, Patent Document 8), liquid crystalline polyester (see, for example, Patent Document 9 and Non-Patent Document 2) and polyester (see, for example, Patent Documents 10 and 11). Any of copolymers including these copolymerization components may be produced by a method of copolymerization by polycondensation of different polymers in the presence of a homopolymer of PPS or a copolymerization component other than PPS having functional terminal groups or by a method of copolymerization by linking polymer terminals. Such methods leave the problem of generation and contamination of the homopolymer and non-uniformity of the block composition in principle.
Patent Document 12 discloses a copolymer with a polyacrylate as a PPS component block-containing copolymer. According to the disclosure of this document, heating a PPS partially having disulfide bonding and an acrylate in the presence of a radical initiator causes a radical chain transfer reaction to the disulfide bonding, so as to obtain a copolymer of PPS and a polyarylate. This technique, however, does not solve the problem with regard to contamination of the homopolymer and the block composition and requires a purification operation for removal of the homopolymer. Additionally, this technique has may other problems in industrial application, such as the poor stability of the disulfide bonding.
In order to solve the problems with regard to the copolymer described above and produce the more homogeneous copolymer, there is a need to obtain a PPS component block or a copolymerization component block other than the PPS component block having the narrower molecular weight distribution than those produced by the conventional techniques. A technique disclosed for production of PPS having the narrower molecular weight distribution is a method using a cyclic arylene sulfide oligomer as raw material and themial polymerization in the presence of or in the absence of a catalyst or an initiator (see, for example, Patent Documents 13 to 15). According to the disclosures of these documents, using the cyclic arylene sulfide oligomer as the raw material allows for production of PPS having the narrower molecular weight distribution, compared with PPS produced by polycondensation. There is, however, no disclosure with regard to the characteristics of a copolymer using this PPS as the component block and its production method.